The invention concerns a catalyst system and procedure for selective alkylation of toluene with propylene.
There are two main methods to industrially produce alkylbenzene. One is Friedel-Crafts-catalyzed alkylation of the ring in aromatic compounds, which has the drawback that it tends to lead to polysubstitution (ring substitution) and, thereby, to a wide product range. The other method is to use base catalysts, such as Li, Na or K metals, in the reaction between aromatic hydrocarbons and olefines. Alkali metals may be used as such, or dispersed on the surface of an inorganic carrier substance. An efficient side chain alkylating catalyst is obtained when metallic sodium is dispersed on the surface of dry potassium carbonate. When a basic alkali metal catalyst is used, alkylation takes place selectively in the side chain of the alkylaromatic and no ring substitution occurs, as is the case with acid Friedel-Crafts catalysts. The drawback is comparatively low selectivity of the alkali metal catalyst to aromatics and its tendency to produce various isomers of alkylbenzene, which have to be separated subsequently. Aliphatic dimers are also produced, although these are easily separated from the alkylbenzenes by distillation.
The selectivity of an alkyl metal catalyst is lowered at the preparation stage by oxygen and water residues in the K.sub.2 CO.sub.3 carrier, whereby oxides and hydroxides are formed from part of the active metal. It is for this reason necessary to dry the carrier well at 120.degree.-150.degree. C. in vacuum for 10-20 hours and to prepare the catalyst in an inert atmosphere or in vacuum.
Martens et al. (Scientific bases for the preparation of heterogeneous catalysts, 4th Internat. Symp., Belgium, 1986, F3.1-3.11, and Preparation and catalytic properties of ionic sodium clusters in zeolites, Nature, 315, (1985), p. 568-470) have suggested that sodium azide (NaN.sub.3) is decomposed at 350.degree.-400.degree. C. to three different modifications: metallic sodium (Na.sub.x.sup.o) crystalline metal clusters (Na.sub.y.sup.o) and ionic clusters (Na.sub.4.sup.3+). When NaN.sub.3 was in this way thermally dispersed on the surface of a zeolite, a basic catalyst was thus obtained which was appropriate for use in isomerizing cis-2-butylene. Of azide and carrier substance either a mechanical mixture was prepared or a methanol suspension, from which the azide was decomposed in a tubular reactor to become sodium on the surface of the carrier.